It is known to utilize the Coriolis reaction of a fluid on a flow tube in order to determine the mass flow through the flow tube. Original developments in this area utilized gyroscopic principles and included a continuous flow tube loop rotated about one axis so as to produce a constant Coriolis force coupled about a separate axis of the flow tube loop. The Coriolis reaction in this type of apparatus is measured by a number of various sensing structures. Pearson U.S. Pat. No. 2,624,198 includes a rotating wheel having a suitable moment of inertia and positioned on the rotating flow tube in such a fashion that the wheel rotates with a force in an opposite direction to the Coriolis force so as to maintain the flow tube in equilibrium. The detecting means which controls the rotation of the wheel continuously corrects the momentum of the wheel so as to correspond to the gyroscopic force of the flow meter. The gyroscopic force varies with respect to the mass flow within the flow tube.
Altfillisch, et al., U.S. Pat. No. 2,813,423 utilizes a rotating flow tube having strain gauges which measure the force of the torque produced by the oppositely directed Coriolis reaction as a function of mass flow.
Roth U.S. Pat. No. 2,865,201, teaches the use of a rigid circular flow tube oscillated about an axis within the plane of the flow tube so as to produce an alternating Coriolis reaction in response to the oscillatory motion. The flow tube in this patent and subsequent related patents utilize circular flow tubes which attempt to simulate the gyroscopic movement of the fluid similar to that found in the previously known rotating flow tube structures. U.S. Pat. No. 3,087,325 utilizes magnetic type sensors which produce a continuously varying signal with respect to the motion of the flow tube and which are compared to the signal of a synchronous detector as a means of calculating the mass flow as a function of the output of the sensors.
Patents to Sipin, U.S. Pat. Nos. 3,355,944 and 3,485,098, teach a projecting U-shaped flow tube which directs the flow through continuous tubing having a partial curvature or a deflection from the axis line formed by the input and output of the flow tube. The flow tube is oscillated transverse to the flow at the point of maximum flow tube deflection with sensors being positioned on opposite side of the substantially U-shaped structure and measure the movement of the flow tube in response to the opposite side Coriolis reaction. Additionally, magnetic vibration velocity sensors are utilized to sense the flow tube motion to determine the mass flow. The additive output of the two sensors is proportional to the amplitude of vibration of the applied oscillation, and the differential output is proportional to the rotational motion of the flow tube due to the Coriolis reaction force.
Cox U.S. Pat. No. 4,127,028 and Smith U.S. Pat. No. 4,187,721 (now reissue patent U.S. Pat. No. Re. 31,450) show optical switches mounted on opposing legs of a fixedly mounted and cantilevered U-shaped flow tubes. The optical switches produce signals in response to the applied oscillation with the time difference between the signals being proportional to the mass flow through the flow tube. The '028 patent utilizes two parallel and adjacently mounted cantilevered flow tubes creating a tuning fork effect with the sensors being mounted on adjacent portions of the two flow tubes to measure the Coriolis reaction with respect to one another at these positions. Flow is provided through each flow tube in the same relative direction and the flow tubes are oscillated in opposite modes. The Coriolis reaction as seen by the sensors on the adjacent flow tubes is substantially doubled, therefore increasing the sensitivity of the mass flow meter.
U.S. Pat. No. 4,422,338 to Smith shows continuously varying analog type sensors similar to the magnetic sensors shown in the Roth and Sipin patents (referred to above), which are mounted on opposite legs of a cantilevered U-shaped flow tube. The mass flow rate is determined as a function of the time separation of the sensor signals with respect to the passage of the flow tube through a plane substantially at the midpoint of the oscillation.